ByHelena Cobban, Special to The Christian Science MonitorApril 21, 1981

Beirut
— The historic south Lebanese port city of Sidon has become the latest victim of artillery battles and factional violence as Israeli-backed Christian militia gunners shelled the town's main street on Easter Sunday.

Sixteen people were killed and 32 wounded, according to official sources.

(On April 20, Israeli planes bombed the Palestinian stronghold of Beaufort Castle in southern Lebanon, according to a Reuters report. Beaufort Castle is a guerrilla stronghold which the Palestinians have used to launch rockets into northern Israel.)

The Sidon shelling cut into restaurants, cinemas, and streets filled with holiday afternoon crowds. It caused a greater number of purely Lebanese casualties in south Lebanon than any other incident in that strife-torn region since the Israeli invasion of March 1978.

But possibly the gravest effect of the shelling, in the long run, was that it brought the specter of sectarian violence openly, for the first time, into the bustling streets of a city of half a million people.

Immediately after the fateful heavy artillery barrage struck home, enraged companions of the victims stormed and tried to burn the local headquarters of the Maronite and Greek Catholic Christian sects.

The militias from whose territory bordering Israel the shells were fired are predominantly made up of members of these two sects. The Israelis openly admit giving military aid to these gunmen, and their colleagues in central and northern Lebanon, on the basis that this is "to help the embattled Christians of Lebanon."

In fact, Sidon and its environs -- like the rest of the country not under the militias' control -- also contain a substantial Christian population, forming perhaps one-third of the total in those areas. Most of these Christians believe they are in no greater danger from the violence that pervades the country than their more numerous Muslim neighbors.

Response from the leftist and Muslim parties predominant in Sidon to the April 19 appearance of anti-Christian sectarianism there was swift. They quickly "discouraged" those responsible for it, and by April 20 were mounting a special protective guard on some Christian sites in the city, local people said.

But some residents, Muslim and Christian, of the mixed-population regions privately expressed concern at the latest outbreak of sectarian unrest.

"Throughout the past six years, with the rightist Christian militias making an issue of religious sect, we have steered nearly clear of sectarianism in our regions," noted one Muslim university professor.

"But now," he added, "everyone in the West, and the Israelis, are making such a fuss about 'saving' the Christians of Lebanon, they are really stoking the fires of hatred. It might rebound on us all, Christians and Muslims.

Some indication that this time, perhaps, the Israeli-backed militias might have gone too far has come from Israeli itself, where militia leader Saad Haddad was reported hospitalized after becoming ill. There is speculation here that his illness is more political than physical, and that his Israeli backers might have taken him out of circulation to reprimand his excess of zeal.

Militia spokesmen have said they shelled Sidon in retaliation for the explosion of a mine in their enclave that killed three militiamen.

Meanwhile, there are other signs that some in Israel's formidable military machine might consider escalating aid to Lebanon's Christian rightist militias.

Leftist military specialists here say only the Israelis, and not their south Lebanese proteges, have the long-range weaponry capable of hitting Sidon from the militias' enclave 1 5 miles away.